1. Field of the Invention
This invention relates generally to lead acid storage cells and batteries, and more particularly, to improved grids for lead-acid storage cells and batteries utilizing raised and lowered elevations, the elevations being in respect to the mean plane formed by the grid, with slits selectively defined through the grid and between said raised and lowered elevations.
The present invention also relates the method of connection of common positive or negative polarity cell grids within a cell and their subsequent connection to succeeding cell members within the internal structure of the battery.
2. Description of the Prior Art
A typical lead-acid secondary battery has an inert casing which contains several cells connected in series and employing a sulfuric acid electrolyte. Each cell is made up of positive and negative plates which are interleaved so that the positive and negative plates alternate. Electrically nonconductive separators, often of a microporous nature, are positioned between plates in order to electrically isolate the positive and negative plates from one another while allowing the free passage of the electrolyte.
Each plate comprises an electrically conductive metal grid, usually made of lead or lead alloy, spread with a layer of "leady oxide" paste. The paste is typically made of a combination of lead oxide, lead sulfate, sulfuric acid, water and other conventionally-used additives used in making chemically active lead-acid storage batteries After the battery grids are pasted with such material, the grids are immersed in a dilute sulfuric acid electrolyte and a direct current is applied to the plates. The application of the current to the plate causes the leady oxide paste on plates connected to the positive terminal of the power source to be substantially transformed to lead dioxide, while the paste on the plates connected to the negative terminal of the power source to be substantially transformed to sponge lead. This process is referred to as "forming" in the art. The resultant lead dioxide and sponge lead materials are referred to as battery "active materials." A battery grid, once it has been pasted, is referred to as a battery plate.
As indicated above, lead dioxide is the chemically active material of positive plates and sponge lead is the active material of negative plates. Both active materials, together with the sulfuric acid electrolyte, react together to form lead sulfate and produce an electric current when an electric circuit is made between positive and negative terminals.
Conventional grids are made completely of lead or lead alloy. They are characterized by having an open mesh or grid-like portion for supporting the active paste materials, a surrounding frame including a top bar for collecting the current developed in the plate, and a terminal lug or tab which is either integral or later connected for joining plates of like polarity together within a cell.
Lead is the preferred grid material since it is resistant to corrosion in the battery environment, it is easy to make a desired grid shape, and it is a fairly good electrical conductor. However, in other grids heretofore, pure lead is so soft that it must be alloyed with hardening elements such as antimony or calcium to form a self-supporting grid strong enough to withstand the current typical mechanized grid pasting and cell assembly operations. Alloying materials in lead add to battery manufacturing cost, and the hardening elements in alloyed lead may interfere with battery life or performance. To meet strength requirements, a substantial amount of lead material is required for each grid. Thus, current battery grids made entirely of lead are relatively expensive and contribute substantially to battery weight.
One previous attempt to provide a relatively lightweight grid used a composite grid consisting of plastics in which strands of wire were embedded. U.S. Pat. No. 3,956,012 to Scholle shows such a grid. However, such grids, although light in weight, suffer from current collecting area and current carrying capacity limitations.
Another composite grid was made by first molding a plastic grid shape and thereafter coating a surface with a layer of lead. U.S. Pat. No. 4,221,854 to Hammar et al illustrates a plastic lead composite grid in which a thin continuous layer of lead or lead alloy sheet is coextensively and adhesively bonded to a thicker layer of plastic However, this grid requires several steps in manufacturing to bond the support layer of plastic to the coextensive layer of lead sheet.
Therefore, there is a need for reduced weight battery grid made of pure lead or substantially pure lead which does not require the need for the introduction of other materials or elements, is easy to manufacture an is able to withstand both the process of preparing battery plates and the rigors of battery use in the field.